This application claims tile priority of Japanese Patent Application No. 399164/1992 filed Dec. 18, 1992, No. 341995/1992 filed Dec. 22, 1992 and No. 348788/1992 filed Dec. 28, 1992, which are incorporated herein by reference.
Automobile wheels or transmission pulleys are formed into a disc part and a peripheral rim part which is roughly perpendicular to the disc part in a unified body. An automobile wheel is once formed into a dish-shaped body having a disc part and an annular part perpendicular to the disc part. The annular part is further shaped into a drop center part (23), an outer rim part (22) and an inner rim part (24), as shown in FIG. 1(a) and FIG. 1(b). A pulley is formed by first forming a dish-shaped body with a central disc part and a peripheral annulus. The annulus is further finished into a rim part which will wear a belt. The dish-shaped prototype is generally formed by several steps of forging, for instance, from a block or a disc (an initial material) of a light metal alloy.
A Prior method disclosed in Japanese Patent Publication No. 3-2574 works a dish-shaped prototype into the final shape by forging, except for an annular part. The peripheral annular part is then formed into a determined rim part by a rolling process. The conventional method requires an extremely high pressure for forging, while the initial material is being transformed into the dish-like body. The dish-like prototype has a central disc part and a peripheral annulus perpendicular to the disc part. The forging process must expand and bend forcibly the peripheral portion of the block or disc initial material toward the annular wall in rams. The initial material resists the deformation in the rams (alternatively called dics or molds). The resistance against expansion is very large. Thus the forging demands an immense pressure. If an initial material were to be deformed only by a single forging process into a dish-like body, the forging would require a huge forging machine, a giant pressing machine for supplying a sufficient pressure to the forging machine and a big ram for enduring the large pressure. The use of large machines is impractical. Thus, the conventional method divides the deformation from an initial block to a dish-like body into several partial processes. Each partial process deforms the material a bit with a small pressure. The reduction of the required pressure in partial processes decreases the size of forging machines.
Poor productivity, however, accompanies the conventional method that includes plural partial processes. The method requires various rams for all partial processes, long processing time from the initial material to the dish-like prototype, and extra time for transferring the bodies between machines. Thus, it takes a long time to produce the wheel having a disc part and a rim part, because the formation of the wheel requires additional process to the dish-like prototype. The divisional, partial processes lowers productivity in producing the wheels.
An object of this invention is to provide a method with fewer steps for shaping a wheel from a metal, plastic material. Another object of this invention is to provide a method of shaping a wheel which can reduce the process time. A still further object of this invention is to provide a method which can reduce the number of rams.